Within distributed safety systems, sensing devices will typically periodically issue safety messages to an associated actuator regarding the states of various sensors. Appropriate response to such safety messages is necessary to ensure optimal and safe operation. For example, in the event a safety message indicates a condition has arisen which may lead to catastrophic failure and unsafe operation unless corrected, it is necessary that the appropriate corrective action (e.g., valve shutoff) actually be taken.
In these distributed safety systems, certain bus integrity methods may be used in an attempt to ensure better or more reliable communication of the safety information over the applicable data bus. These methods have included various error checking and coding schemes for detecting and correcting data errors arising within the data communicated via the data bus. For example, a safety message may contain a check sum or cyclic redundancy code (CRC) to detect bit errors. In addition, while particular bus systems, such as the Process Field Bus (“PROFIBUS”) communication protocol and system, may employ various error coding methods in order to identify erroneous data, such systems are generally unsuitable for applications involving safety messages.
Moreover, the increasing automation of network-based industrial processes and control systems has rendered such systems vulnerable to attack by computer “hackers”, i.e., those individuals engaging in malicious code breaking. For example, it is conceivable that hackers may attempt to disrupt process operation by falsely emulating or interfering with the various safety messages transmitted among a distributed arrangement of sensors and actuators. In extreme circumstances, such interference could result in unsafe process operation and potentially dire attendant consequences.